SpeedTree 9 Shader error when opening a project

https://unity.slack.com/archives/C6Y79CZM0/p1710790550283199

Adding null check to avoid the error, like other Shaders.

Author: YohannVaastUnity

Packages/com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/HDRenderPipelineAsset.DefaultResources.cs

@@ -53,10 +53,10 @@ public partial class HDRenderPipelineAsset
         #region SpeedTree
 
         /// <summary>HDRP default speed tree v8 shader</summary>
-        public override Shader defaultSpeedTree8Shader => defaultShaders.defaultSpeedTree8Shader;
+        public override Shader defaultSpeedTree8Shader => defaultShaders?.defaultSpeedTree8Shader;
 
         /// <summary>HDRP default speed tree v9 shader</summary>
-        public override Shader defaultSpeedTree9Shader => defaultShaders.defaultSpeedTree9Shader;
+        public override Shader defaultSpeedTree9Shader => defaultShaders?.defaultSpeedTree9Shader;
 
         #endregion